A tablet PC, or pen computer, is a notebook or slate-shaped mobile computer, equipped with a touch screen or graphics tablet/screen hybrid technology that allows the user to operate the computer with a stylus, digital pen, or fingertip instead of a keyboard or mouse. Tablet PCs offer a more natural form of input, as sketching and handwriting are a much more familiar form of input than a keyboard and mouse, especially for people who are new to computers. Tablet PCs can also be more accessible because those who are physically unable to type can utilize the additional features of a tablet PC to be able to interact with the electronic world. Applications often do not know they are running on a tablet PC, and the operating system may attempt to provide input to applications that appears similar to mouse input. This can cause several problems for screen magnifiers used in conjunction with tablet PCs or other touch-based interface devices.
Screen magnifiers are a type of assistive technology used by visually impaired people with some functional vision. By magnifying areas of the screen, the screen magnifier allows people that would otherwise not be able to see areas of the screen that are too small to enlarge these areas. Screen magnifiers are software applications that present a computer's graphical output in an enlarged form. Many screen magnifiers act similar to a physical magnifying glass that a user can move around over the screen to magnify a specific area, except rather than a physical object the screen magnifier is software and the user moves the displayed glass or lens with the mouse or other input device. The most common method of magnification is to present an enlarged view of a portion of the original screen content that covers a portion of or the entire screen. The enlarged view often tracks the pointer or cursor as the user moves a mouse or other input device around the screen so that the user can magnify different areas. Screen magnifiers may work with a single application or across multiple applications at the operating system level. For example, Microsoft Windows Vista includes a magnifier application for magnifying the entire desktop and any applications displayed on it.
Because the view is enlarged, screen magnifiers provide a way to move the lens, or magnified area, to different areas of the desktop or application. For example, at a magnification factor of 4 times (4×), only one-eighth of the desktop can be shown in a full screen magnifier at a time. Thus, to see the other three-fourths of the desktop a user moves the magnified area around in a process called panning. Although panning often refers only to horizontal movement (and scrolling or other terms refer to vertical movement), panning and movement as used herein refer to movement of the magnified view in any direction, whether horizontally, vertically, or diagonally.
It is easy to move a screen magnifier in response to mouse input, because a mouse moves continuously from one point of the screen to another. For example, as user cannot move the cursor with a mouse from the lower left of the screen to the upper right of the screen without passing through the points in between. The same is not true of a natural input device like a digital pen or touch input. The user can pick up the natural input device at one location and set it down again at a location far from the original location. The cursor often jumps from place to place as the user picks up and sets down the digital pen. This makes the experience of moving a screen magnifier that is following the cursor very disconcerting because the magnification of the screen contents makes the jump feel even larger as more pixels scroll across the screen very quickly. In addition, for quick touches the operating system may not even send a hover or other message that indicates the cursor's new position, so that the magnifier does not move. The user can become disoriented and not know what part of the desktop or application the user is viewing after repeatedly picking up and setting down the pen.
In addition, if the user is trying to click on an item displayed in the UI (e.g., a file in a file management application) using a digital pen and the screen magnifier is jumping to align with the new pen location, then it can make it difficult for the user to select the intended item. This can lead to the user selecting the wrong item or simply being confused. Some screen magnifiers do not alter input such that a user must actually click at an item's original location to select the item, not necessarily where the item appears in the magnifier. If the user is trying, for example, to drag a file from one side of the magnifier lens to the other (or from within the magnifier lens to a folder or other location outside of the lens), the user may miss selecting the target item that the user intended.